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Watts to Amps Calculator

Convert between watts, amps, and volts.

Mason ReidFounder and Lead Estimator at MeasureThen

Last updated 2026-08-21

What Is a Watts to Amps Calculator?

A watts to amps calculator converts electrical power into current so you can size wire and breakers. It divides watts by voltage for single phase circuits and by 1.732 times the voltage for three phase circuits. Use it when a device is rated in watts but you need the amperage for your panel.

How It Works

Amps = Watts ÷ Voltage (single-phase) or Watts ÷ (1.732 × Voltage) (three-phase).

Example

2,400 W at 120 V single-phase = 20 A. 10,000 W at 240 V three-phase ≈ 24.1 A.

How to Calculate

  1. Enter the device power in watts, for example 2,400 W for a large appliance.
  2. Enter the system voltage, commonly 120 V for standard household circuits.
  3. Choose single phase. The tool divides watts by volts, so 2,400 ÷ 120 equals 20 A.
  4. For three phase equipment, for example 10,000 W at 240 V, it divides by 1.732 × 240, giving about 24.1 A. Note this assumes a resistive load with a power factor of 1.

Common household loads

ApplianceTypical wattsAmps at 120 V
LED light10 W0.08 A
Refrigerator600 W5 A
Microwave1,200 W10 A
Space heater1,500 W12.5 A
Electric dryer5,000 WAbout 21 A at 240 V

Sources

Frequently Asked Questions

Why multiply by 1.732 for three-phase?

1.732 is the square root of 3, the factor relating line-to-line voltage and three-phase power.

When do I use the three-phase option?

For commercial motors and larger equipment wired on three-phase services.

Does this account for power factor?

No — it assumes a resistive load (power factor = 1). Motors and inductive loads draw more current.

Estimate the cost with the Electrical Cost Calculator or browse Electrical Calculators

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Mason ReidFounder and Lead Estimator at MeasureThen

Mason Reid founded MeasureThen after two decades of hands-on work in construction and estimating. Across residential and light commercial projects, he sized concrete pours, framed walls, hung drywall, and priced out roofing, fencing, and deck work — learning the exact math that every job depends on. At MeasureThen he writes the formulas, checks every calculator against real-world assumptions, and makes sure each one is simple enough for a homeowner to trust and a contractor to use. When he is not measuring twice, he is helping projects stay on budget.

Every MeasureThen calculator uses simple, transparent formulas and standard industry assumptions drawn from common construction practice. We show the math behind each result and include worked examples so you can follow along and double-check the numbers. Results are estimates: materials, labor, and pricing vary by region and market, so always confirm important figures with a licensed professional and your local building codes.